This invention relates to an air regulator for an impact wrench for use in fastening or unfastening bolts or nuts. More specifically, this invention relates to the impact wrench having an improved air regulator for regulating air flow to an air motor.
A known air regulator of this type included in an impact wrench is disclosed in Japanese Laid-Open specification No. 1-321174. This air regulator comprises an adapter valve secured to an air supply slot of a handle, a cylindrical regulator valve movably fitted on a periphery of the cylindrical regulator, said adaptor valve having air slots, said regulator valve having air supply slots of different diameters with a regular interval. When the regulator valve is operated, the air supply slot of a desired diameter is adapted to communicate selectively with the desired air slot, so that the air flow to an air motor can be regulated. However, according to the air regulator of this type, an air supply reversing means is needed to be provided in the air supply pass to make the air motor rotate reversely, which results in a complicated construction of the air regulator. Conventionally, there are some types of impact wrenches for fastening or unfastening bolts or nuts. One type of the impact wrenches is an all-purpose impact wrench, which is used for both fastening and unfastening bolts or nuts.
Normally, an unfastening operation requires a more increased toque than a fastening operation, for example, because there is some rust on bolts or nuts. For this reason, taking into account a torque necessary for unfastening bolts or nuts, a torque of the all-purpose impact wrench is determined. Accordingly, a fastening torque of the all-purpose impact wrench exceeds a specified fastening torgue. Therefore, an excessive torque is applied to fasten bolts or nuts. Thus, when unfastening bolts or nuts again, a more excessive torque is needed. In this way, a fastening torque to be applied to bolts or nuts becomes gradually more increased, which may cause deformation and breakdown of a structure. Also, a fastening torque exceeding a tolerance of a fastening bolt may cause failure of the fastening bolt.
To solve such problems, two kinds of an unfastening impact wrench and a fastening impact wrench can be used to unfasten and fasten bolts or nuts. However, the use of the two kinds of impact wrenches causes a higher cost and a longer fastening/unfastening operation, which leads to a troublesome operation.
Another type of the conventional impact wrench is a torque-adjusting impact wrench. In one type of the torque-adjusting impact wrench a control valve is adjusted to change a rotational speed of a pneumatic motor. In this type of the impact wrench the adjusting operation is complicated and an adjusted torque varies widely. In another type of the torque-adjusting impact wrench a twisted shaft is provided between an anvil shank and a driving shaft to adjust a torque. However, in this type of the impact wrench a structure of a hammer mechanism becomes complicated and expensive. In another type of the torque-adjusting impact wrench a pneumatic control circuit, a hydraulic control circuit, or an electric control circuit is provided to control a fastening torque automatically within a maximum torgue. However, in this type of the impact wrench the control circuit becomes complicated.